Currently, when a copolymer of a conjugated diene monomer and an aromatic vinyl monomer is prepared through typical anionic polymerization, organolithium is used as an anionic polymerization initiator.
In anionic polymerization, a polar solvent such as tetrahydrofuran or dimethylether is generally utilized to prevent aggregation of the initiator and to increase reactivity. For example, JP 2746053 B2 discloses a method of preparing poly(p-tert-butoxy-styrene) using sec-butyllithium as a polymerization initiator and a polymerization solvent comprising tetrahydrofuran. However, this preparation method is disadvantageous because additional equipment is required for the separation process for recovering n-hexane, attributable to the addition of the polar solvent.
Furthermore, butyllithium is problematic upon anionic polymerization because H in the main chain of the polymer is extracted due to high anionic reactivity, undesirably causing side reactions such as the production of branch structures.